yeah id be mad too if I was a canon shooter and my second's images were much better in terms of DR, color and bit depth

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"Much better" will it be only when you see two images and can easily say which was taken by which camera. THEN we can talk about one being "much better" than the other. Please don't provoke meaningless flamewars if we can prevent it...

Yeah: the question remains: Can the Canon 5 D Mark 3 shoot in Manual exposure mode, with AUTO ISO enabled, with Exposure Compensation used? Not in Av mode, as T. Campbell mentioned works, but in Manual exposure mode. Can the 5D-III do Manual exposure in AUTO ISO mode and allow the shooter use Exposure Compensation? The Canon guy in the video claims NO, it can not.

I'm not sure what more you need.. The video claims it's not possible and I told you what to do in such case - use ISO instead. Exposure compensation would do exactly the same, so I'm not sure what's the big deal. Have your ISO on Auto and if it gets it wrong, dial it back/more a little to compensate, exactly like you'd do with the function you're asking about.
You should be familiar with this technique anyway. If the feature won't be available to you, what will you do? Don't rent the camera?

Think about it, the camera must use the meter to pick an ISO. All you've done is lock down two of three settings. If Canon really disabled exp. comp, in M mode while using Auto ISO, it simply doesn't make sense.

but that still doesn't answer the question.

all I can find from the internets:

In Manual exposure mode, a pre-set shutter speed and lens aperture can be continually maintained, even if the light changes. This allows the photographer to have full control over stopping motion and depth-of-field, while still allow the camera to react to any changes in light (this could be ideal in remote-controlled or intervalometer shooting). A very handy, yet underutilized, feature is the ability to apply AE Lock when working with Auto ISO in Manual mode. The viewfinder will show the difference between the locked value and the current metered value. It is important to know that the camera won't let you use the “ealxtended” ISO settings (equivalent to ISO 50, 51200 and 102400 on the EOS 5D Mark III and EOS 6D) in Auto ISO.

Click to expand...

from manual:

if Auto ISO is set, the ISO Speed setting Will Change to suite the Shutter Speed and aperture to obtain a standard exposure: Therefore, you may not obtain the desired exposure effect.

Click to expand...

this suggests no exp. comp.

this article suggests no too:

The EOS 5D Mark III camera and others can limit the range of ISO settings that the camera can use for auto ISO. This would enable the EOS 5D Mark III to meet Jon’s needs.

But then Jon added another tweet with the notion of being able to use exposure compensation with Auto ISO in manual mode. Since using Auto ISO has in effect turned manual exposure in to an automatic exposure mode, therefore it makes sense to be able to bias the exposure with exposure compensation. Unfortunately the EOS 5D Mark III does not allow this. I think that a firmware update could certainly make it possible, but none has come from Canon.

At the moment the following cameras can work in manual mode with auto ISO and still have exposure compensation…

EOS-1D X

EOS-1DX Mark II

EOS 5DS / EOS 5DS R

EOS 7D Mark II

EOS 80D

You can either access the exposure compensation using the Q button to change the setting on the rear LCD, but there is a faster way.

Yeah: the question remains: Can the Canon 5 D Mark 3 shoot in Manual exposure mode, with AUTO ISO enabled, with Exposure Compensation used? Not in Av mode, as T. Campbell mentioned works, but in Manual exposure mode. Can the 5D-III do Manual exposure in AUTO ISO mode and allow the shooter use Exposure Compensation? The Canon guy in the video claims NO, it can not.

Click to expand...

I rented a 5D mk III this weekend as a second body. For football, I will use manual mode and auto ISO on my 7D mk II and then use EC, so I wanted to set up the 5DmkIII this way as well. What I found was it would do exposure bracketing but I could not find out how to be able to use EC. It wasn't the end of the world but it is something that I would really liked to have been able to use.

Have your ISO on Auto and if it gets it wrong, dial it back/more a little to compensate, exactly like you'd do with the function you're asking about.

Click to expand...

Here's the problem with this statement: You're telling him to dial it back. That's exactly what he wants to do via exp. comp, so the ISO is adjusted by whatever stop. What is he supposed to "dial back"? The shutter speed and aperture he doesn't want to give up. Come on man...

To do what you're asking means the user would have to turn off auto ISO, then change the ISO manually to match the desired exposure, OR meter on something that changes the ISO to the desired level, then lock the EV.

Have your ISO on Auto and if it gets it wrong, dial it back/more a little to compensate, exactly like you'd do with the function you're asking about.

Click to expand...

Here's the problem with this statement: You're telling him to dial it back. That's exactly what he wants to do via exp. comp, so the ISO is adjusted by whatever stop. What is he supposed to "dial back"? The shutter speed and aperture he doesn't want to give up. Come on man...

To do what you're asking means the user would have to turn off auto ISO, then change the ISO manually to match the desired exposure, OR meter on something that changes the ISO to the desired level, then lock the EV.

Click to expand...

Please, re-read what I wrote. That's exactly what I said. He's supposed to change ISO manually if Auto doesn't cut it. All I'm talking about is ISO, as exposure compensation in M works exactly like that - manipulating ISO... It doesn't matter if you change ISO or exposure compensation, it will do exactly the same thing = it doesn't matter if the camera supports exposure compensation in M or not.

Think about it, the camera must use the meter to pick an ISO. All you've done is lock down two of three settings. If Canon really disabled exp. comp, in M mode while using Auto ISO, it simply doesn't make sense.

but that still doesn't answer the question.

all I can find from the internets:

In Manual exposure mode, a pre-set shutter speed and lens aperture can be continually maintained, even if the light changes. This allows the photographer to have full control over stopping motion and depth-of-field, while still allow the camera to react to any changes in light (this could be ideal in remote-controlled or intervalometer shooting). A very handy, yet underutilized, feature is the ability to apply AE Lock when working with Auto ISO in Manual mode. The viewfinder will show the difference between the locked value and the current metered value. It is important to know that the camera won't let you use the “ealxtended” ISO settings (equivalent to ISO 50, 51200 and 102400 on the EOS 5D Mark III and EOS 6D) in Auto ISO.

Click to expand...

from manual:

if Auto ISO is set, the ISO Speed setting Will Change to suite the Shutter Speed and aperture to obtain a standard exposure: Therefore, you may not obtain the desired exposure effect.

Click to expand...

this suggests no exp. comp.

this article suggests no too:

The EOS 5D Mark III camera and others can limit the range of ISO settings that the camera can use for auto ISO. This would enable the EOS 5D Mark III to meet Jon’s needs.

But then Jon added another tweet with the notion of being able to use exposure compensation with Auto ISO in manual mode. Since using Auto ISO has in effect turned manual exposure in to an automatic exposure mode, therefore it makes sense to be able to bias the exposure with exposure compensation. Unfortunately the EOS 5D Mark III does not allow this. I think that a firmware update could certainly make it possible, but none has come from Canon.

At the moment the following cameras can work in manual mode with auto ISO and still have exposure compensation…

EOS-1D X

EOS-1DX Mark II

EOS 5DS / EOS 5DS R

EOS 7D Mark II

EOS 80D

You can either access the exposure compensation using the Q button to change the setting on the rear LCD, but there is a faster way.

Click to expand...

silly Canon.

Click to expand...

Finally got the answer!

I would try to go for Mark IV instead. My Nikon cropped sensor has auto ISO with EC and many a times it captures me the moments. So I would better go for Mark IV which has this option.

Yeah: the question remains: Can the Canon 5 D Mark 3 shoot in Manual exposure mode, with AUTO ISO enabled, with Exposure Compensation used? Not in Av mode, as T. Campbell mentioned works, but in Manual exposure mode. Can the 5D-III do Manual exposure in AUTO ISO mode and allow the shooter use Exposure Compensation? The Canon guy in the video claims NO, it can not.

Click to expand...

I rented a 5D mk III this weekend as a second body. For football, I will use manual mode and auto ISO on my 7D mk II and then use EC, so I wanted to set up the 5DmkIII this way as well. What I found was it would do exposure bracketing but I could not find out how to be able to use EC. It wasn't the end of the world but it is something that I would really liked to have been able to use.

Click to expand...

Thank you for clearing my doubt! Though it is not mandatory to have EC, it gives a comfort and adjusts ISO much faster than manual adjustment.